Pulmonary epithelium is divided into three histopathologically distinct compartments: bronchi, bronchioli, and alveoli. Our aim is to characterize the cellular differentiation and genetic damage associated with progression of premalignant changes in each compartment. 1) Morphologic atypias. Using resection specimens from lung cancer patients, we have shown that morphologic changes may proceed independently during field cancerization. In the alveolar compartment, where most of the adenocarcinomas originate, candidate early lesions included bronchiolization of alveoli (BOA). We established a classification system for BOA and are studying its molecular basis. 2) Peripheral airway cell (PAC) and neuroendocrine (NE) differentiation. We have shown that field cancerization in lung is also characterized by alterations in the expression patterns of PAC and NE markers. Using Clara cell specific protein (CC10) mRNA as a PAC marker of progenitor cells in non-neoplastic and neoplastic airway epithelium, we identified a novel alveolar metaplasia, whose malignant potential is now examined. We have also shown that a neural transcription factor human achaete- schute homolog-1 is expressed in human lung, providing a unique tool to assess the role of NE differentiation in the bronchiolar compartment. 3) Oncogenes and tumor suppressor genes. We combined PCR analyses with microdissection and noted frequent chromosome 3p abnormalities throughout the lesions, including BOAs and alveolar metaplasias, suggesting that these changes occur early in carcinogenesis. A novel approach using in situ PCR reaction was developed for topographic genotyping of p53 and K-ras alterations which appear to be later events. The significance of the project is that the results will provide a rational basis for early detection and intervention in human lung carcinogenesis by identifying specific markers as well as models how to approach multistep epithelial carcinogenesis.